The present invention relates to a device for treating a continuously advancing material web via an ultrasound generator having a sonotrode, including a counter-tool which lies opposite the face of the sonotrode. The material web passes through a gap between the sonotrode and the counter-tool. A drive sets the sonotrode against the counter-tool.
This general type of device is described in German Patent 195 26 354 C1. The treatment includes, for example, bonding of a non-woven made of thermoplastic fibers, by bonding the fibers at certain points. In order to achieve an optimum treatment effect, the distance between the sonotrode and the counter-tool, i.e. the sheath surface of the relief which is applied to it, in some instances, must be very accurately maintained. For this reason, a sensor is provided in known devices, which detects the height of the gap between the sonotrode and the counter-tool, and the signal of which is used to regulate the distance. Precise and reliable detection of the gap height is a difficult process, however, and requires a complicated measurement device.
Maintaining a certain gap height must be done in such a precise way because temperature variations at the sonotrode and the accompanying thermal expansions play a significant role. For this reason, the device according to German Patent 195 13 246 C2 includes a sensor which detects the temperature of the sonotrode, the signal of which is used to influence the gap height. However, only one partial aspect of the variable which changes the gap height is detected in this manner, i.e. only the temperature-related displacements.
Other important changes which influence the gap height in operation and occur with greater frequency result from concentricity defects of the counter-roller that generally forms the counter-tool, as well as irregularities of the material web itself.
The present invention is based on the task of improving adherence to a uniform treatment effect.
The present invention provides an apparatus for treating a continuously advancing material web via an ultrasound generator having a sonotrode, including a counter-tool which lies opposite the face of the sonotrode. The material web passes through a gap between the sonotrode and the counter-tool. A drive sets the sonotrode against the counter-tool. Additionally, means are provided for suppressing the effect of vibrations at the sonotrode on the treatment of the material web.
The invention is also directed to the problem of minimizing the irregularities with greater frequency, which are attributable to vibrations in the ultrasound treatment system. Such vibration-related irregularities can come about by excitation of many different types, for example as a result of the movements of the counter-roller, as mentioned, due to concentricity defects, of entraining effects of the material web which act on the face of the sonotrode, crosswise to it, as bending stress, etc.
Accordingly, implementation of the principle of the invention has different aspects.
One important aspect is to prevent the vibrations excited by impacts of the textile web on the sonotrode from occurring in the first place. This concern is addressed by an additional aspect of the invention, in which the sonotrode is supported, in its vibration direction, via a high-frequency actuator, which is activated by a control which reacts to measured changes in the force or the distance between the face of the sonotrode and the counter-tool. The high-frequency actuator serves to prevent changes in the distance between the face of the sonotrode and the counter-roller, to a certain extent, by retracting the sonotrode in timely manner, for example, if the counter-roller is demonstrating eccentricity, so that no sudden compression of the material web occurs and this reason for vibrations is therefore avoided. This involves not only eccentric counter-rollers, but also irregularities in the web, for example.
The actuator must be able to react very quickly, in accordance with the speed of the occurrence of such changes in distance between the sonotrode face and the counter-roller. A piston/cylinder unit activated with a liquid pressure medium is not capable of this.
For this reason, the high-frequency actuator is also provided in addition to such a piston/cylinder unit which might be present and has the task of bringing about the larger setting movements of the sonotrode.
Possible high-frequency actuators are piezoelectric or magnetostrictive actuators, which can perform the strokes in the millisecond or microsecond range which is in question here. Piezoelectric actuators have been described in the essay xe2x80x9cPiezo-Aktuatoren fxc3xcr den mm-Bereichxe2x80x9d [piezo actuators for the mm range] by Tonshoff and Laux in the VDI-Z Special Antriebstechnik [special issue of the journal of the Society of German Engineers, concerning drive technology], April 1994, pages 48 to 52, and in an application example in German Patent 43 25 143. Magnetostrictive actuators have already been proposed to control the nozzle needle in injection valves, in German Patent PS 695 974. The contents of these references are hereby incorporated by reference for these teachings.
If the drive of the sonotrode includes a piston/cylinder unit to press the sonotrode against the counter-tool, i.e. the counter-roller, another measure to suppress vibrations can be to damp them by throttling, i.e. to place throttles in the feed lines to the two cylinder chambers, which throttle the flow of the pressure medium.
In order not to have to overcome break-away forces in the piston/cylinder unit, it is recommended to seal it not with piston rings or the like, but rather with a roll membrane.
In known embodiments, the sonotrode is surrounded, on its circumference, by a bearing unit which engages at the location of a vibration node, seen in the axial direction of the sonotrode. Either the sonotrode has a circumference flange and the bearing unit has an inside circumference groove, into which the circumference flange engages, or vice versa. In either case, elastic rings are provided between the flanks of the circumference flange and the circumference groove, which are supposed to damp the coupling between the sonotrode and the bearing unit in the axial direction and reduce the transfer of ultrasonic vibrations in this direction to the bearing construction.
However, these elastic intermediate elements themselves normally promote the formation of vibrations. In order to be able to bring about an adaptation of the vibration behavior, it is recommended, according to a further embodiment of this invention, to make the axial prestress force of the rings adjustable. One way of doing this is for a hydraulic or pneumatic piston/cylinder unit to be provided, by means of which the rings can be pressed together axially.
The sonotrode projects freely downward from the clamping location, against the counter-roller or the counter-tool. The material web moves crosswise to the sonotrode, which rests against the material web with a certain force. This results in an entrainment tendency of the material web, which can give rise to bending vibrations of the projecting end of the sonotrode.
For this reason, it is recommended that the sonotrode be supported near its face without impairing the mobility of the sonotrode in its axial direction.
Finally, the tendency toward vibration at the sonotrode can also be reduced in that it does not have a face located parallel to the material web, so that the material web runs up against the edge of the face, but rather the face of the sonotrode is open, in wedge shape, relative to the incoming material web, so that in a way, a constantly narrowing intake mouth is formed.